An Evaluation of the Effects of Benzotriazole in NH 4 OH Slurry for Copper CMP
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An Evaluation of the Effects of Benzotriazole in NH4OH Slurry for Copper CMP V.S.C. Len, D.W. McNeill and H.S. Gamble School of Electrical & Electronic Engineering, The Queen’s University of Belfast, Belfast BT9 5AH, Northern Ireland
ABSTRACT Chemical mechanical polishing (CMP) of copper using alumina-based NH4OH slurry containing benzotriazole (BTA) has been evaluated in terms of polish efficiency and viability. Dishing of damascene copper patterns can result from a combination of chemical dissolution and mechanical abrasion due to the deformed polishing pad bending into the recessed copper regions. The addition of at least 0.1 wt.% BTA to the slurry leads to the formation of a thin Cu(I)-BTA polymer on the copper surface during CMP. This polymer reduces the amount of dishing by an order of magnitude. At the same time, however, the CMP polish rate falls sharply with the addition of 0.1 - 0.25 wt.% BTA to the slurry. Above 0.25 wt.% BTA, the polish rate falls no further. Stability of alumina particles in the NH4OH slurry is found to deteriorate with the addition of BTA. Integrated copper/barrier electromigration resistance test structures with large contact areas (2x2mm) have been successfully patterned using a 2-step CMP/etching process scheme, using a BTA-containing slurry to minimise dishing.
INTRODUCTION CMP has become an essential technique for patterning copper multi-level metallisation (MLM) as device sizes continue to shrink below the current 0.18-micron technology. Problems such as dishing in copper lines and erosion of the inter-layer dielectric are major obstacles in achieving a successful damascene copper process. The copper in the recess trenches is susceptible to dishing, especially during the overpolish step of at least 10%. Thus, some preventative measure is desirable to protect the copper surface in the trench areas during polish steps. Pioneering copper CMP work using alkaline and acidic slurries with oxidants such as oxygen, ferricyanide ((Fe(CN)63-) and hydrogen peroxide (H2O2) was carried out and reported by Steigerwald et al. [1,2,3]. Other copper CMP slurry chemistries in various media and problems related to these chemistries were investigated by Carpio et al. [4]. Luo and co-workers [5,6] studied the incorporation of BTA in the slurry and the related slurry stability in acidic and alkaline media. BTA works as an inhibiting agent by reacting with the copper surface or native oxide to form a Cu(I)BTA polymer. This polymer can prohibit water, acids and alkalis from the metal surface [7] and offers excellent corrosion protection in harsh conditions [8]. The viability of copper CMP using alumina-based NH4OH slurry with and without the addition of BTA is examined. A brief study of the stability of alumina particle suspension in both slurries is also presented.
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EXPERIMENTAL DETAILS A modified Lapmaster lapping machine with a 14” diameter Suba IV/IC1000 stacked pad was used to perform copper CMP. The platen was driven at a fixed rotation speed of 60 rpm and the superimposed wafer carrier
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